1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, particularly to an electrophotographic photosensitive member containing a disazo pigment.
2. Description of the Prior Art
Heretofore, electrophotographic photosensitive members utilizing an inorganic photoconductive material such as selenium, cadmium sulfide, zinc oxide, etc. as the photosensitive component have been known.
On the other hand, since discovery of specific compounds exhibiting photoconductivity, a large number of organic photoconductive materials have been developed. For example, there have been known organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, etc., organic photoconductive materials of low molecular weights such as carbazole, anthracene, pyrazolines, oxadiazoles, hydrazones, polyarylalkanes, etc., organic pigments or dyes such as phthalocyanine pigments, azo pigments, cyanine dyes, polycyclic quinone pigments, perylene type pigments, indigo dyes, thioindigo dyes or squaric acid methyne dyes, etc. Particularly, organic pigments or dyes having photoconductivity can be synthesized more easily than inorganic materials, and yet variation in selecting a compound exhibiting photoconductivity at an appropriate wavelength region can be expanded. For such reasons, a large number of proposals about photoconductive organic pigments or dyes have been made. For example, electrophotographic photosensitive members employing disazo pigments exhibiting photoconductivity as the charge generation substance in the photosensitive member separated in functions into the charge generation layer and the charge transport layer have been known, as disclosed in U.S. Pat. Nos. 4,123,270, 4,247,614, 4,251,613, 4,251,641, 4,256,821, 4,260,672, 4,268,596, 4,278,747 and 4,293,628.
The electrophotographic photosensitive member employing such an organic photoconductive material can be produced by coating by suitable selection of a binder, and therefore is very high in productivity and can provide inexpensive photosensitive members. Moreover, by selection of an organic pigment, the photosensitive wavelength region can be freely controlled. On the other hand, in spite of such advantages, this photosensitive member involves drawbacks in sensitivity and durability characteristics, and only a few have been practically applied up to date.